Reforming process



United States Patent 3,434,959 REFORMING PROCESS Merritt C. Kirk, Jr.,Claymont, Del., assignor to Sun Oil Company, Philadelphia, Pa., acorporation of New Jersey Filed June 7, 1967, Ser. No. 644,321 Int. Cl.Cg 39/00; C07c 3/50 US. Cl. 208-62 7 Claims ABSTRACT OF THE DTSCLOSUREThis invention relates to the production of high octane gasoline. Theprocess of the present invention is a combination process in whichnormal butane recovered from an alkylation process effluent, is charged,along with petroleum naphtha, into a reforming process. The normalbutane is substantially isomerized therein to isobutane which isrecovered and added to the feed to the alkylation process.

When hydrocarbons boiling in the naphtha range are reformed in thepresence of a dual function catalyst, 21 number of reactions take place,including dehydrogenation of naphthenes to the corresponding aromatics,dehydrocyclization of parafiins to aromatics, hydrocracking to lowermolecular weight products, and isomerization of paraflins. The overallreaction is endothermic with a typical fuel requirement of 200,000 to300,000 B.t.u. per barrel of feed. The extent of naphthenedehydrogenation, a very desirable reaction, is increased by hightemperatures and low partial pressures of hydrogen.

Addition of normal butane to the reforming charge stock, as contemplatedby this invention, results in several advantages. The normal butane issubstantially isomerized in the reforming zone to isobutane, a reactionwhich is exothermic and reduces to a small extent the fuel requirementsfor interheating between reaction zones. The added butanes reducehydrogen partial pressure which increases the rate and extent ofdehydrogenation of naphthenes. This advantage is accomplished withoutlowering the purity of the product hydrogen since the butanes producedare easily condensed therefrom. Finally, the present invention providesisobutane feed for alkylation from normal butane, an advantage ofconsiderable magnitude in refineries where the isobutane is notabundant.

United States Patents 2,428,417, Gary, and 2,293,705, Bloch, disclosethe isomerization of normal butane to isobutane for addition to analkylation feed, but neither of these patents shows the isomerization asan incident to naphtha reforming in a reforming zone. The Gary patent isconcerned with balancing the isobutane to butylene ratio in thealkylation feed stock by obtaining additional butylene through theconversion of normal butane into isobutane by catalytic isomerizationfollowed by the conversion of isobutane to butylene by pyrolysis. Thisscheme serves a system which is deficient of butylene rather thanisobutane. The Bloch patent is concerned with using sulfuric acid forboth the purification of the butane and for alkylation.

Cooke Patent 2,358,149 discloses a thermal reforming process whichcharges a light naphtha mixed With recycled C and C hydrocarbons. Theaddition of the C and C hydrocarbons permits operation of the processunder conditions which elfect high yields without the heavy formation ofcarbon on heating units. Cooke points out that his invention is arefinement utilizing this expediency of C and C hydrocarbon additionwhich expediency was first developed by Ostergaard, Patent 2,135,- 014.The Ostergaard patent points out that the C and C hydrocarbons includeboth saturated and unsaturated constituents. The saturated ingredientsare dehydrogenated, under the conditions of the thermal reforming, tounsaturated constituents which polymerize or alkylate. Since the presentinvention charges only normal butane to the naphtha stock undergoingreforming, and since the conditions of the catalytic reforming of thepresent invention are different from those of the thermal conversion,the added light hydrocarbon undergoes isomerization rather thandehydrogenation and polymerization.

Patent 3,003,949, Hamilton, discloses, as part of an overall scheme forproducing high octane gasoline, the addition of C hydrocarbons, from areformate, to the feed to an alkylation. The patent does not teachadding normal butane, from the alkylation product, to the reformer feed.

Patent 2,288,336, Welty et al., teaches that reforming a feed containinglower boiling hydrocarbons decreases hydrogen consumption and therebyincreases catalyst life. By low boiling hydrocarbons the Welty et al.patent means those boiling in the range between an initial boiling pointof 111 F. up to between about 60 and percent off at 300 F. This fractionwould include no hydrocarbons lighter than C Conventionally the C andlighter hydrocarbons are removed from the reformer feed. It has beenfound, that significant conversion of normal butane to isobutane willtake place in the reforming zone to provide feed additive for chargeinto an alkylation reactor. The present invention is particularlyadvantageous where isobutane alkylation feed is in short supply.

The present invention is described as a process for producing highoctane gasoline which comprises subjecting a feed to catalytic reformingin the presence of a platinum on alumina catalyst, said feed comprisinga naphtha and a normal C hydrocarbon stream. The normal C hydrocarbonstream used in the reforming has been recovered from the product of analkylation step which will be described below. The product recoveredfrom the reforming step contains significant amounts of isobutane, atleast a portion of which has resulted from the isomerization of theadded normal butane during the catalytic reforming. The isobutane isseparated from the reformate and is added to an isobutane-deficientalkylation feed. The enriched alkylation feed is then subjected toalkylation conditions to give a product which contains saturatedhydrocarbons suitable for use as motor fuel components and some normalbutane. Most of the normal butane has been introduced in the alkylatefeed and has passed through the alkylation zone unconverted. The normalbutane is separated from the alkylate and is recycled as the normal Chydrocarbon stream introduced into the first step reforming of theprocess of this invention.

Under the conditions of the reforming step, the normal butane issubstantially converted into isobutane although it would not necessarilybe expected that this conversion would take place to any degree becauseof the short residence times of the reforming feed in the reforming zoneand because of the conditions in the zone. It has been found though thateven with the residence times of reforming, there is between about 30percent to 50 percent conversion of normal butane to isobutane. Thisconversion provides isobutane which can be alkylated with butylene underalkylating conditions. The present invention is, therefore, mostadvantageously utilized to proivde isobutane for alkylation athydrocarbon refineries which are normally deficient in isobutane.

Furthermore the conversion of the normal butane to isobutane providescertain advantages to the reforming step of the process of thisinvention. The isomerization is exothermic and reduces fuel requirementsfor interheating between reforming zones. With the addition of thenormal butane, the hydrogen partial pressure is reduced and the rate ofdehydrogenation of naphthenes and the overall extent of dehydrogenationare increased so that a reformate of improved properties is produced.This latter advantage is achieved without any lowering of the purity ofthe hydrogen produced since the butanes can be easily separated from thereformate gas efliuent.

Suitable conditions for reforming naphtha are well known in the art andthis step may comprise any known or suitable reforming procedure whichutilizes a dual function catalyst. The reforming of the presentinvention can be applied to any hydrocarbon feed stock suitable forcatalytic reforming, most preferably a light naphtha stock boilingbetween about 120 F. and 390 F. The catalyst used in this step ispreferably any of the conventional type platinum-on-alumina catalystswhich generally contain between about 0.1 to 2.0 percent platinum.Catalysts of this type are available commercially and are extensivelydescribed in the literature. The compositions may include various activeforms of alumina, such as gamma, eta, and kappa, and the aluminas mayvary considerably in surface characteristics depending upon how thecatalyst was made. The combination of platinum and the alumina producesa catalysts having a plurality of functions whereby such reactions asdehydrogenaiton, isomerization, cyclization and hydrocracking arepromoted. In some cases a minor amount of a halogen, such as chlorine orfluorine, is incorporated in the catalyst to control the catalyticactivity for promoting certain types of these reactions.

In reforming naphtha or gasoline stocks with the catalyst the conditionscan be varied rather Widely; thus temperatures of about 600 to about1050 F. are suitable and the preferred range is from about 800 to about950 F. Within these temperature limits weight space velocities of about0.05 to about 10.0 pounds of naphtha, per hour, per pound of catalyst inthe reaction zone may be employed advantageously; however, spacevelocities of about 0.25 to about 5.0 provide the best results. Hydrogenshould be introduced into the reforming reactor at rates running fromabout 0.5 to about 20.0 mols of hydrogen per mol of hydrocarbonreactants. The hydrogen is in admixture with the normal butane added inthe present invention. The normal butane is added in a ratio of about0.5 to about 5.0 mols of butane to naphtha reactant. While the totalreaction pressure in the reforming may be maintained at any valuebetween about 50 and about 1000 pounds per square inch gauge (p.s.i.g.),the best results are obtained by holding the reaction pressure withinthe range between about 100 and about 750 p.s.i.g. In any event, thereaction conditions should be adjusted to effect a net production ofhydrogen in the reaction.

The alkylation step of the present invention can be any one of a numberof alkylation processes well known in the art. This step can be athermal alkylation at high temperatures, about 900 F., and pressures,600 to 3000 p.s.i.g. with a contact time of about minutes. However,catalytic alkylation is the preferred method for this step. This processcan be conducted using either sulfuric acid or hydrogen fluoride ascatalyst. In the alkylation, sulfuric acid concentration is maintainedat about 90 percent and hydrogen fluoride concentrations usually arebetween 80 and 90 percent. With sulfuric acid, the product quality isimproved with reduction in temperature to the range 32 to 50 F. Asuitable temperature control can be obtained by evaporation of thereactants at the site of reaction. With hydrogen fluoride the process isless sensitive to temperature, and temperatures of 32 to about F. can beused. Some form of heat removal is essential, since the heat of reactionis approximately 600 b.t.u. per pound of butylene. In order to preventpolymerization of the butylene as charged, a large amount of isobutaneshould be present in the reaction zone. Isobutane-to-butylene mol ratiosof 8 to 1 are common, but side reactions can be suppressed moreeffectively by use of larger ratios up to 14 to l. The alkylationreaction depends on a two-phase system with a low solubility of theisobutane in the catalyst phase. In order to insure intimate contact ofreactants and catalyst, efficient mixing with fine subdivision isprovided.

The drawing illustrates one embodiment of the present invention. In thedrawing a light naphtha is mixed with normal butane from line 18 and isfed via line 1 into the reforming zone 2. Heat input into the reformingZone is indicated at 3. A reformate containing substantial amounts ofisobutane is transferred via line 4 to a high pressure separator 5 wherea gaseous recycle stream is separated. The gaseous recycle is removedfrom the high pressure separator 5 through line 6. The reformate istransferred from the high pressure separator 5 through line 7 to astabilizing zone 8 where the light ends are removed via line 9 toproduce a stabilized reformate via line 10. C s are recovered from thelight ends at zone 11 with the remaining light hydrocarbons passing outline 12 and C s passing via line 13, to be mixed with an alkylation feedin line 14. The alkylation feed comprises butylene and isobutane but isdeficient in isobutane necessary to give best results in the alkylationzone 15. The isobutaneenriched feed and recycle isobutane from line 20are subjected to alkylation conditions in zone 15. The alkylationefliuent is removed via line 16 to zone 17 where isobutane and n-butaneare recovered. Normal butane is recycled via line 18 to be admixed withthe reformer feed in line 1. Isobutane is recycled to alkylation zone 15via line 20. An alkylate boiling in the gasoline boiling range isrecovered from the separator zone 17 via line 19.

The following example illustrates the invention:

A light naphtha fraction boiling between and 210 F. is mixed with anormal butane stream at about 2 mols of normal butane per mol ofnaphtha. The mixture is fed into a reforming zone where it is contactedwith platinum catalyst deposited on an eta alumina base containing about1 percent combined fluorine. The temperature in the reformer ismaintained at about 850 to 875 F. and the pressure at about 400 p.s.i.g.The liquid hourly space velocity is at about 3. Hydrogen is added to thefeed in such an amount that the hydrogen to hydrocarbon mol ratio isabout 7 to 1. Effluent from the reforming zone is subjected to a highpressure separation which removes gas for recycle. Liquid from the highpressure separation zone is then stabilized. Isobutane recovered fromthe light ends from the stabilizer are condensed and added to analkylation feed containing isobutane and butylene in mol ratio of 5to 1. This isobutane is added at such a rate as to give anisobutane-to-butylene mol ratio in the enriched feed of about 10 to l.The enriched feed is fed into the alkylation zone, at a rate such as toprovide a residence time of 30 minutes, where it is contacted withconcentrated sulfuric acid at a temperature of about 40 F. and at apressure slightly above atmospheric. A product, containing 23 Weightpercent 2,2,4 trimethylpentane and 35 percent trimethylpentanes otherthan 2,2,4, is recovered in the alkylate along with 3 weight percentnormal butane which is recycled to be mixed with the reformer feed.

The example shows that normal butane can be isomerized to isobutaneunder reforming conditions and in admixture with the reforming feed. Theexample also shows that the isobutane recovered from the reformate canbe used as make up isobutane in alkylation feed deficient in isobutane.

What is claimed is:

1. A process for producing high octane gasoline which comprises:

(a) subjecting a feed to catalytic reforming, said feed comprising anaphtha and a hereinafter specified normal butane stream;

(b) recovering a reformate of improved gasoline characteristicscontaining isobutane at least a portion of which has resulted from theisomerization of said butane stream during said reforming;

(c) separating a stream containing at least a portion of said isobutane;

(d) charging said separated stream from step (c), mixed with analkylation feed comprising butylene, isobutane and normal butane, intoan alkylation zone under alkylating conditions to alkylate the isobutanewith butylenes to obtain an alkylation product comprising saturatedhydrocarbons suitable for use as a motor fuel component and normalbutane;

(e) separating said normal butane from said alkylation product; and

(f) recycling said normal butane from step (e) as said normal butanehydrocarbon stream in step (a).

2. The process of claim 1 in which step (a) comprises subjecting saidfeed to catalytic reforming in the presence of a platinum on aluminacatalyst at a temperature of about 600 to 1050 F. and at a weight spacevelocity of about 0.05 to about 10.0 pounds of feed per hour per poundof catalyst and with the addition of hydrogen to said reforming at arate from about 0.5 to about 20.0 mols of hydrogen per mol of feed.

3. The process of claim 2 in which step (a) comprises subjecting saidfeed to catalytic reforming in the presence of a platinum on aluminacatalyst at temperatures of about 800 to 950 F. and at a weight spacevelocity of about 0.25 to about 5.0 pounds of feed per hour per pound ofcatalyst.

4. The process of claim 3 in which in step (d) the alkylation is carriedout in the presence of a sulfuric acid catalyst.

5. The process of claim 3 in which in step (d) the alkylation is carriedout in the presence of a hydrogen fluoride catalyst.

6. The process of claim 4 in which in step (d) the alkylation is carriedout at temperatures between about 32 to about F. and at a mol ratio ofisobutane to butylene of between about 8 to 1 and about 14 to 1.

7. The process of claim 5 in which in step (d) the alkylation is carriedout at temperatures between about 32 to about F. and at a mol ratio ofisobutane to butylene of between about 8 to 1 and about 14 to 1.

References Cited UNITED STATES PATENTS 2,871,277 1/1959 I-Iaensel260683.65 3,003,949 10/ 1961 Hamilton 20879 DELBERT E. GANTZ, PrimaryExaminer.

T. H. YOUNG, Assistant Examiner.

U.S. Cl. X.R. 260-68311

